The present invention relates generally to refrigeration systems and more specifically relates to refrigeration systems that use a Stirling cooler in cooperation with a thermosiphon as the mechanism for removing heat from a desired space.
In the beverage industry and elsewhere, refrigeration systems are found in vending machines, glass door merchandisers (xe2x80x9cGDM""sxe2x80x9d) and other types of dispensers and coolers. In the past, these units generally have used a conventional vapor compression (Rankine cycle) refrigeration apparatus to keep beverages or containers cold. In the Rankine cycle apparatus, the refrigerant in the vapor phase is compressed in a compressor so as to cause an increase in temperature. The hot, high-pressure refrigerant is then circulated through a heat exchanger, called a condenser, where it is cooled by heat transfer to the surrounding environment. As a result of the heat transfer to the environment, the refrigerant condenses from a gas back to a liquid. After leaving the condenser, the refrigerant passes through a throttling device where the pressure and temperature of the refrigerant are reduced. The cold refrigerant leaves the throttling device and enters a second heat exchanger, called an evaporator, located in or near the refrigerated space. Heat transfer with the evaporator and the refrigerated space causes the refrigerant to evaporate or change from a saturated mixture of liquid and vapor into a superheated vapor. The vapor leaving the evaporator is then drawn back into the compressor so as to repeat the cycle.
Stirling cycle coolers are also a well known as heat transfer mechanisms. Briefly, a Stirling cycle cooler compresses and expands a gas (typically helium) to produce cooling. This gas shuttles back and forth through a regenerator bed to develop much greater temperature differentials than may be produced through the normal Rankine compression and expansion process. Specifically, a Stirling cooler may use a displacer to force the gas back and forth through the regenerator bed and a piston to compress and expand the gas. The regenerator bed may be a porous element with significant thermal inertia. During operation, the regenerator bed develops a temperature gradient. One end of the device thus becomes hot and the other end becomes cold. See David Bergeron, Heat Pump Technology Recommendation for a Terrestrial Battery-Free Solar Refrigerator, September 1998. Patents relating to Stirling coolers include U.S. Pat. Nos. 5,678,409; 5,647,217; 5,638,684; 5,596,875 and 4,922,722, all incorporated herein by reference.
Stirling cooler units are desirable because they are nonpolluting, efficient, and have very few moving parts. The use of Stirling cooler units has been proposed for conventional refrigerators. See U.S. Pat. No. 5,438,848, incorporated herein by reference. The integration of a free-piston Stirling cooler into a conventional refrigerated cabinet, however, requires different manufacturing, installation, and operational techniques than those used for conventional compressor systems. See D. M. Berchowitz et al., Test Results for Stirling Cycle Cooler Domestic Refrigerators, Second International Conference. As a result, the use of the Stirling coolers in, for example, beverage vending machines, GDM""s, and other types of dispensers, coolers, or refrigerators is not well known.
Another known heat transfer device is a thermosiphon. In general, a thermosiphon is an efficient closed loop heat transfer system that uses a phase change refrigerant. The thermosiphon may have a condenser end and an evaporator end. In the condenser end, heat is transferred out of the phase change refrigerant so as to turn the gas to a liquid. The liquid travels by the force of gravity to the evaporator end where heat is again added so as to change the liquid back to a gas. The gas then rises and returns to the condenser end. The process is repeated in a closed cycle.
To date, the use of a thermosiphon in beverage vending machines, GDM""s, beverage dispensers, or similar types of refrigerated devices is not well known. Likewise, the use of a thermosiphon with a Stirling cooler is not well known. Both devices, individually and in combination, however, may provide increased efficiencies in terms of performance, energy demands, and overall operating costs.
A need exists therefore for adapting Stirling cooler technology to conventional beverage vending machines, GDM""s, dispensers, and the like. Likewise, there is a need for adapting Stirling cooler technology to thermosiphon technology in general and to conventional beverage machines, GDM""s, dispensers, and the like.
The present invention thus provides an enclosure for a refrigerated space. The enclosure may include a thermosiphon and a Stirling cooler. The thermosiphon may include a condenser end and an evaporator end. The ends may be connected by a small diameter pipe and a large diameter pipe. The Stirling cooler may drive the thermosiphon to cool the refrigerated space.
Specific embodiments of the present invention may include the use of a phase change refrigerant in the thermosiphon. The phase change refrigerant may be carbon dioxide. The small diameter pipe may have a diameter of about 0.5 to about 3 millimeters and the large diameter pipe may have a diameter of about 3 to about 10 millimeters. The condenser end may include a condenser positioned adjacent to the Stirling cooler. The condenser may include a condenser block and/or a number of condenser coils. The evaporator end may include an evaporator such as a fin and tube evaporator. The Stirling cooler may include a cold end and a hot end, with the cold end in contact with the thermosiphon. A number of thermosiphons and a number of Stirling coolers may be used. An air movement device also may be used so as to force air through the refrigerated space and the evaporator end of the thermosiphon.
A further embodiment of the present invention may provide for a refrigerator, such as a glass door merchandiser. The refrigerator may include an insulated frame. The insulated frame may include a refrigerated space and a refrigeration deck area. A removable refrigeration deck may be positioned within the refrigeration deck area. The removable refrigeration deck may include a thermosiphon and a Stirling cooler. The insulated frame may include a number of walls defining the refrigeration deck area. The walls may further define a baffle area. A drain hole may extend between the refrigeration deck area and the baffle area. An air passageway may extend between the refrigerated space and the refrigeration deck area.
The thermosiphon may include a condenser end and an evaporator end. The condenser end may include a condenser positioned adjacent to the Stirling cooler. The evaporator end may include a fin and tube type evaporator. A number of thermosiphons and a number of Stirling coolers may be used.
The refrigeration deck also may include a top plate. The refrigeration deck may include a means to mount the Stirling cooler to the top plate. The top plate may be an insulated spacer. The top plate may include a number of apertures therein for airflow therethrough and a handle thereon so as to remove the refrigeration deck. The refrigeration deck also may include an air movement device.
The refrigerator also may include an insulated box surrounding the thermosiphon and the Stirling cooler. The refrigeration deck area may have a first set of rails positioned therein while the insulated box may have a second pair of rails positioned thereon such that the insulated box may be slid in and out of said refrigeration deck area.
A further embodiment of the present invention provides for a refrigeration deck for a refrigerated space. The refrigeration deck may include a plate. A Stirling cooler may be mounted to the plate and a thermosiphon may be connected to the Stirling cooler. The plate may be an insulated spacer. The plate may include a number of apertures therein for airflow therethrough and a handle thereon so as to remove the refrigeration deck. The refrigeration deck also may include an air movement device. The Stirling cooler may include a cold end and a hot end. The plate may include an aperture therein such that the cold end of the Stirling cooler is positioned on a first side of the plate and the hot end of the Stirling cooler is positioned on the second side.
The thermosiphon may include a condenser block positioned on the cold end of the Stirling cooler. The condenser block may include a mounting flange formed thereon. The refrigeration deck may include an attachment ring attached to the mounting flange so as to join the condenser block and the cold end of the Stirling cooler. The plate also may include an indentation surrounding the aperture. The refrigeration deck may include a vibration mount positioned within the indentation and supporting the mounting flange and the Stirling cooler. The vibration mount may include a ring of elastomeric material. The aperture may include an insulation ring positioned therein.
The thermosiphon also may include a number of condenser coils positioned about the cold end of the Stirling cooler. The Stirling cooler may include an outer casing with a number of flanges extending therefrom. The refrigeration deck may include a number of isolation mounts so as to connect the flanges of the Stirling cooler to the plate. The isolation mounts may include several cylinders of an elastomeric material. The aperture may include an insulation ring positioned therein.
The refrigeration deck also may include an insulated box defined by the plate. Either the plate or the insulated box may have a pair of guide rails positioned thereon. The plate may have a condenser aperture positioned therein so as to position the Stirling cooler. The plate also may have a fan aperture therein so as to position the fan.
The method of the present invention may cool an enclosure with a thermosiphon. The thermosiphon may have a phase change refrigerant therein, a condenser positioned adjacent to a cold end of a Stirling cooler, and an evaporator. The method may include the steps of removing heat from the phase change refrigerant at the condenser by the Stirling cooler so as to turn the phase change refrigerant to a liquid, flowing the phase change refrigerant to the evaporator, forcing air past the evaporator and into the enclosure so as to cool the enclosure, adding heat to the phase change refrigerant at the evaporator by the forced air so as to turn the phase change refrigerant to a vapor, and rising the phase change refrigerant to the condenser.
Other objects, features, and advantages of the present invention will be come apparent upon review of the following specification, when taken in conjunction with the drawings and the appended claims.